Although electric discharge, supersonic waves, a laser, and the like can be used to machine a micro hole, precision machining using a micro drill has been most widely used to date. This is because processing using the micro drill has advantages in that it is used to machine a deeper hole than any other method, produces a hole having excellent precision in straightness, roundness, parallelism, surface roughness, etc., and facilitates a finishing process that follows the machining. In particular, in the electronics and computer industry, micro hole-machining technology is generally used in machining a PCB, a mask, which is used in the fabrication of an Integrated Circuit (IC), etc. In response to the increasing degree of integration of Large-Scale Integrated circuits (LSIs), higher machining precision and higher productivity are required to be realized for various reasons such as the fining of a machining hole, an increase in the depth with respect to the diameter of a machining hole (i.e., the aspect ratio), high density of circuit boards, etc. As the competition to develop micro components in which high functions are integrated is becoming intense, the importance of the micro hole-machining technology is increasing every day.
Such a micro drill is generally divided into a drill part, which machines a hole, and a shank part, which is fixed to a chuck of a high revolution motor. A fabrication method of the related art includes preparing a round rod having a predetermined diameter by sintering a super-hard material and shaping the round rod such that it has a drill part and a shank part. In this fashion, the entire portion of the micro drill is made of the super-hard material. However, the fabrication cost increases if more super-hard material is used, since the super-hard material is expensive. Therefore, in order to reduce the cost, a method of preparing a drill part, which is made of a super-hard material, preparing a shank part, which is made of stainless steel, for example, STS 420J, and coupling the shank part to the drill part made of the super-hard material has been introduced.
As an example of the method of fabricating the micro drill by making the drill part and the shank part of different materials, as shown in FIG. 1, a method of machining a hole 62, into which a super-hard rod 80 can be fitted, in a shank part 60, press-fitting the super-hard rod 80 into the hole 62 at a high temperature using a heating device 70, and finally machining a drill blade 82 is widely used.
This method of the related art can reduce the use of the super-hard material by a certain amount because the shank part is made of stainless steel. However, this method still causes a large amount of loss in the super-hard material, since the final diameter of the machined drill blade 82 is in the range from 0.1 mm to 0.4 mm, whereas the diameter of the super-hard rod 80 is about 1.5 mm. In addition, since the stainless steel used in the shank part is generally a brittle material having high hardness, it is more expensive to form the hole 62, into which the super-hard rod is intended to be fitted, in the shank part 62 than in common steel materials. Furthermore, in order to fit the super-hard rod into the shank part, it is required to finely machine the hole 62 according to the diameter of the super-hard rod. However, it is very difficult to form a fine hole having a diameter of 1 mm or less in the super-hard stainless steel, and heating to a high temperature is required to couple the super-hard hard material to the shank.